Methanethiol SAMs Induce Reconstruction and Formation of Cu⁺ on a Cu Catalyst under Electrochemical CO₂ Reduction

Abstract

Cu electrode-based electrochemical CO 2 reduction using renewable energy is a promising method for conversion of CO 2 to useful compounds such as methane, ethylene, and ethanol. Heteroatom-doped and/or -derived Cu as oxide-derived Cu has been investigated in context of development of a stable catalyst with high selectivity, whereas the role of heteroatoms is not yet well understood. It is not known whether heteroatoms act as a moiety of the catalyst or simply induce reconstruction of the catalyst. This work is an investigation of the role of the heteroatom in electrocatalytic CO 2 reduction with a Cu electrode modified with methanethiol monolayers (MT−Cu), which is able to distinguish the presence of heteroatom contamination originating from electrolyte or air. Controlled potential electrolysis of CO 2 using an MT−Cu electrode at −1.8 V at Ag/AgCl exhibits greater selectivity for C 2 products than an unmodified polycrystalline Cu electrode (bare Cu). On the other hand, a sulfur-modified Cu (S−Cu) electrode predominantly generates formate as a CO 2 reduction product. In an investigation of the mechanism, an in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy instrument is used as a powerful surface analyzer. Scanning electron microscopy, grazing-incidence wideangle X-ray scattering (GIWAXS), and X-ray spectroscopy (XPS) are also employed in the investigation. The spectroscopic data show that reconstruction and formation of Cu + on the Cu surface occur at negative potential greater than −1.4 V vs Ag/AgCl by electrochemical reduction of methanethiol monolayers. DFT calculations are also performed under conditions close to the experimental conditions of electrical bias and aqueous electrolyte. The results indicate that a roughened surface is favorable for generating C 2 products. In addition, the Cu + moiety promotes generation of C 2 products, demonstrating that the doped heteroatom plays a crucial role in electrochemical CO 2 reduction.

Effects of the Catalyst Dynamic Changes and Influence of the Reaction Environment on the Performance of Electrochemical CO2 Reduction

“…introduced methanethiol monolayers to the Cu electrode to induce the formation of Cu(I) in the electrode. [ 148 ] Lee et al. fabricated Cu 2 O via electrodeposition, and they found that Cu 2 O remains on the surface of catalysts under CO 2 R condition, which is attributed to be the origin of the high selectivity toward CH 4 .…”

“…[147] Moreover, Masuda et al introduced methanethiol monolayers to the Cu electrode to induce the formation of Cu(I) in the electrode. [148] Lee et al fabricated Cu 2 O via electrodeposition, and they found that Cu 2 O remains on the surface of catalysts under CO 2 R condition, which is attributed to be the origin of the high selectivity toward CH 4 . [58] Overall, it is clear that there is a strong correlation between the existence of Cu(I) species and the high selectivity toward the further reduced product, for example, CH 4 , C 2 H 4 , however, explicit mechanistic understanding behind this effect is still pending.…”

Electrocatalytic CO2 reduction to ethylene over ZrO2/Cu-Cu2O catalysts in aqueous electrolytes

“…3b). 40,41 The Zr XPS spectra revealed that Zr 4+ was the main Zr species in the ZrO 2 /Cu-Cu 2 O catalyst, which is confirmed by the two peaks at 185.5 eV and 182.9 eV attributed to 3d 3/2 and 3d 5/2 of Zr 4+ , respectively (Fig. 3c).…”

Electrochemical Reduction of Carbon Dioxide to Ethanol: A Review

“…There are many reported examples having varied molecular structures and ligands extensively used by many scientists in this field. [57,62,63,116,117] For example, cobalt(III) triphenylphosphine corrole (Cocorrole) complex was demonstrated by Gonglach et al. [57] This Co-corrole complex contains three polyethylene glycol residues attached at the meso-phenyl groups.…”

“…Functionalizing metal based electro-catalysts with different surface ligands is an effective way to enhance ECO 2 R performance. Iijima et al [116] reported Cu electrode modified with methanethiol monolayers (MTÀ Cu) for ECO 2 R. The roughened surface and the Cu + moiety, generated due to methanethiol during ECO 2 R, promote C 2 product formation. The Ni II complex with free amine functional group [Ni II L NH2 ] was also reported for ECO 2 R. [62] The Ni II complex produced ethanol with 49 % FE at À 1.60 V (vs. Ag/AgCl).…”